The present invention relates to a bowl mill with a vertically powered milling bowl that milling cylinders roll over inside a milling space, which is surrounded by a housing, whereby there is an annular air box, which communicates with the milling space, below the milling bowl and whereby there is an outlet aperture in the floor of the air box and an evacuator extends through the air box.
The evacuator or stripper in a bowl mill of this type, known for example from Aufbereitungstechnik 12, 537-49 (1971), is rigidly attached to the driven milling-bowl support. The evacuator accordingly rotates at the same speed as the milling bowl. The function of the evacuator is to force coal dust and foreign bodies that get into the air box from the milling space out through the outlet aperture.
If the supply of hot air in a mill of this type is suddenly interrupted as the result for instance of a malfunction in the combustion space of the boiler supplied by the mill, the coal dust in the milling space at that particular moment will drop out of the milling bowl. Some of it will even get into the air box 8 and lead to malfunction in the equipment.